Acclimatisation is defined as adapting to new surroundings. Weeds are any non-native plant species, introduced either deliberately or accidentally, that have become naturalised. The earliest recorded attempts to intentionally introduce plants to Tasmania were by English and French navigators. Captain James Cook visited Adventure Bay, Bruny Island in 1777, and his crew planted potatoes, kidney beans, peach and apricot kernels, which apparently did not survive. In 1792, Admiral Bruny d'Entrecasteaux's crew planted cabbages, potatoes and sorrel at Recherche Bay. In January 1793, the botanist Labillardière on the vessel Recherche reported that only a few plants were still surviving, all in poor condition. This second attempt to introduce plants to Tasmania was also apparently unsuccessful.

The arrival of Europeans in Tasmania, and the establishment of Hobart in 1804, brought farming practices, animal husbandry and an associated influx of new plants, which included crops, ornamentals and also many weeds. Charles von Hügel recorded that by the 1830s in Hobart, European weeds were well established and had replaced much of the existing native flora. By 1838, a vast number of flowering plants, both native and introduced, were available to gardeners in the colony. In the 1840s the first superintendent of the Royal Society's Gardens introduced over 250 species in sixty genera.

In the 1850s and 1860s acclimatisation societies were established throughout Australia and New Zealand to introduce 'useful' plants and animals into the new colonies. The rules of the Tasmanian Acclimatisation Society stated that 'The objects of the Society shall be the introduction, acclimatisation and domestication of all innocuous quadrupeds, … and vegetables, whether useful or ornamental'. Many additional species were introduced into the Royal Society's gardens (later to become the Royal Tasmanian Botanical Gardens) at this time.

There was little recognition of the threat posed by new plant introductions into the state. Harvey noted the spread of thistles, blackberries and briar in Tasmania, and it was only in the early 1870s, with the Act to prevent the spread of the Californian Thistle (Carduus arvensis, current name: Cirsium arvense [L.] Scop.), that the threat posed by new weeds to agricultural land was formally recognised.

Many of the plants that were brought in for agriculture, and for use as ornamentals by the early settlers, also became established as weeds. The first comprehensive census of the naturalised flora in Tasmania was completed in 1878, and over one hundred species were considered naturalised. The naturalised plants included many agricultural and ruderal (growing near human habitation in waste places) weeds that are predominantly of European origin. Most of these plants are annuals and rapidly maturing perennials, and a few woody plants, for example, gorse, blackberries and briar, are represented.

The most recent census of the weed species in Tasmania, published in 1999, lists over 740 species that were naturalised at that time. Currently approximately one third of Tasmanian Flora is introduced. A census of the current Tasmanian Flora, which includes naturalised species, is available at www.tmag.tas.gov.au/Herbarium.